The present invention is directed to a piston for use in a tool dispensing a mass from a foil bag. The piston has a central engagement part engageable with one end of an axially extending piston rod which displaces the piston. A wipe-off edge at least partially surrounds the central engagement part and projects radially outwardly from it.
Single or multi-component hardenable or curable masses are used for a great variety of applications, especially in the building construction industry. Such masses are commercially available in cartridges or foil bags and the mass is pressed out of the cartridge or foil bag by an appropriate dispensing tool.
A piston of such a dispensing tool is disclosed in the German patent publication P 42 31 420.8 and is made up of two individual pistons each having a central engagement part shaped in a cambered manner at its end face and a wipe-off edge projecting radially outwardly from and laterally enclosing the engagement part.
The piston is double acting and is located in a cylindrically shaped cassette part arranged to receive the foil bag with the cassette part forming a part of the dispensing tool, or, as an alternative, it can be placed into the tool as a separate part. The double-acting piston is displaceable in the cassette part. A piston rod with a thrust member axially displaces the piston. The cassette part is open at its opposite ends. After the contents of the foil bag are completely pressed out, the foil bag is in a collapsed condition and can be removed from the cassette part and a new foil bag filled with mass can be placed in the cassette part, however, in the opposite end of the cassette part from the piston. After the cassette part is aligned in position in the dispensing tool, it is inserted into the tool so that the next dispensing operation can be initiated.
A foil bag is collapsed or folded up in the course of pressing-out the mass and is at least partially received in the peripheral region about the central engagement part. Accordingly, the piston is designed so that each individual piston has a storage space in the outer circumferential region of the central engagement part extending from the end face region of the individual piston to the wipe-off edge.
Accordingly, the known piston has two storage spaces arranged axially in tandem and separated from one another by the wipe-off edges. The axial length of the piston depends upon the corresponding length of the storage spaces. As a result, the considerable required length for the storage spaces affects the overall length of the piston, the length of the cassette part and also the length of the dispensing tool itself.